The chorion genes of Drosophila melanogaster provide an excellent system for the study of the genetic control of morphogenesis. Through the use of cDNA clones as well as genomic clones from the major chorion gene regions, the basic parameters of chorion gene structure and expression during oogenesis will be determined. This knowledge will be used to analyze the mechanisms which give rise to abnormal chorion gene expression in specific mutants such as ocelliless and in newly selected mutant strains. The preparation of antibodies to the major chorion proteins will allow the definition of the structural role played be each in the eggshell. In combination with studies of the abnormal chorions in mutant strains lacking single chorion proteins, information on the assembly of a morphological structure will be obtained. Thus we hope ultimately to understand mechanisms that control the expression of a related set of genes during development, and how alterations in the normal program of expression, through their effects on an assembly process, give rise to mutant phenotypes.